This study's objectives were to extend understanding of how long- duration air blast (from megaton weapons) interacts with fires ignited by the thermal pulse. It was postulated earlier that extinguishment would occur, for many materials, when subjected to such long-duration flows. Tests were designed and conducted in the URS Long Duration Flow Facility at Fort Cronkhite, Calif. Burning materials were placed in a room (approximately 12' x 15' x 8.5') and subjected to pressures of 1.0 to 3.5 psi, flows of 200 to 600 ft/sec and attendant flow durations of 1 to 2 sec. Materials tested included, but were not limited to, paper (solid-pack and crumpled), cloth, vinyl, cardboard, and wood. In addition, two tests(without fire) of a simulated EOC (without blastdoors) were performed at 2 psi. Results indicated that 2 psi (rather than 2.5 psi predicted) is a boundary for extinguishment of lighter materials, such as paper and cardboard. Those materials which readily support smouldering combustion, such as cotton batting and heavy cloth, do not extinguish even at 3.5 psi. EOC test results indicated potentially severe damage to communications equipment, monitoring equipment, and furniture.